Happiness is an attitude to life as a whole, while joy lives in the moment. As J. D. Salinger once said: “Happiness is a solid, joy is a liquid.” Happiness is something you pursue. But joy is not. It discovers you. It has to do with a sense of connection to other people or to God. It comes from a different realm than happiness. It is a social emotion. It is the exhilaration we feel when we merge with others. It is the redemption of solitude.
Chief Rabbi Sacks
The Pursuit of Joy (Ki Tavo 5775)
https://rabbisacks.org/the-pursuit-of-joy-ki-tavo-5775/#_ftn2
The Nature of the Shelamim Sacrifice, Prof. Yonatan Grossman translated by Nechama Barach
(א) מצוה לשמח ברגלים - לשמח ברגלים, שנאמר (דברים טז יד) ושמחת בחגך, והענין הראשון הרמוז בשמחה זו הוא, שנקריב שלמים על כל פנים בבית הבחירה, וכענין שכתוב וזבחת שלמים. והדר ושמחת בחגך. ובשביל הקרבת השלמים אמרו זכרונם לברכה (חגיגה ו, ב) נשים חיבות בשמחה, לומר שאף הן חיבות להביא שלמי שמחה. ועוד אמרו זכרונם לברכה (שם ח א) שמח בכל מיני שמחה, ובכלל זה הוא אכילת הבשר ושתית היין, וללבוש בגדים חדשים, וחלוק פרות ומיני מתיקה לנערים ולנשים, ולשחק בכלי שיר במקדש לבד, וזו היא שמחת בית השואבה הנזכרת בגמרא (סוכה נ א), כל זה שזכרנו בכלל ושמחת בחגך. ואמרו זכרונם לברכה במסכת פסחים (קט, א) חיב אדם לשמח בניו ובני ביתו ברגל, ושם נאמר, תניא, רבי יהודה בן בתירה אומר בזמן שבית המקדש קים אין שמחה אלא בבשר, שנאמר (דברים כז ז) וזבחת שלמים וגו'. עכשיו אין שמחה אלא ביין, שנאמר (תהלים קד טו) ויין ישמח לבב אנוש. ואמרו עוד במה משמחן? אנשים בראוי להם ביין, ונשים בראוי להם בבגדים נאים, והזהירתנו התורה כמו כן להכניס בכלל השמחה העניים והגרים והחלושים, שנאמר אתה והלוי והגר והיתום והאלמנה.
(ב) משרשי המצוה. לפי שהאדם נכון על ענין שצריך טבעו לשמח לפרקים, כמו שהוא צריך אל המזון על כל פנים, ואל המנוחה ואל השנה, ורצה האל לזכותנו, אנחנו עמו וצאן מרעיתו, וצונו לעשות השמחה לשמו למען נזכה לפניו בכל מעשינו. והנה קבע לנו זמנים בשנה למועדים, לזכר בהם הנסים והטובות אשר גמלנו, ואז בעתים ההם צונו לכלכל החמר בדבר השמחה הצריכה אליו, וימצא לנו תרופה גדולה, בהיות שובע השמחות לשמו ולזכרו, כי המחשבה הזאת תהיה לנו גדר לבל נצא מדרך הישר יותר מדאי, ואשר עמו התבוננות מבלי החפץ בקטרוג ימצא טעם בדברי.
(ג) מדיני המצוה. כתבתי קצתן למעלה. ויתר פרטיה, במסכת חגיגה ובמקומות מן הגמרא בפזור.
(ד) ונוהגת מצוה זו לענין השמחה, אבל לא לענין הקרבן בכל מקום ובכל זמן בזכרים ונקבות. והעובר על זה ואינו משמח עצמו ובני ביתו והעניים כפי יכלתו לשם מצות הרגל בטל עשה זה, ועל הדרך שזכרנו יאמרו זכרונם לברכה (אבות פ''ב מי''ב) וכל מעשיך יהיו לשם שמים.
(1) The commandment to rejoice on the festivals: To rejoice on the festivals, as it is stated (Deuteronomy 16:14), "And you shall rejoice on your holiday." And the first matter that is hinted in joy is that we offer peace-offerings regardless at the Choice House. And [this] is like the matter that is written (Deuteronomy 27:7), "And you shall offer peace-offerings" and it continues, "and you shall rejoice on your holiday." And [concerning] the offering of peace-offerings, they, may their memory be blessed, said (Chagigah 6b), "Women are obligated in joy" - meaning that even they are obligated to bring peace-offerings of joy. And they, may their memory be blessed, also said (Chagigah 8a), "Rejoice in all types of rejoicing." And included in this is the eating of meat and the drinking of wine, to wear new clothes, the distribution of fruit and types of sweets to the youths and the women and to play musical instruments in the Temple alone - and that is the joy of the drawing house (simchat beit hashoeva) that is mentioned in the Gemara (Sukkah 50a). All that we mentioned is included in "And you shall rejoice on your holiday." And they, may their memory be blessed, said in Tractate Pesachim 109a, "A man is obligated to gladden his children and the members of his household on a festival." And it is said there, "It was taught, Rabbi Yehuda ben Beteira says, 'At the time when the Temple is standing, joy is only with meat, as it is stated (Deuteronomy 27:7), "And you shall offer peace-offerings, etc." Now [...] joy is only with wine, as it is stated (Psalms 104:15), "And wine gladdens the heart of man."'" And they said further, "With what should one make them rejoice? Men with what is fit for them, with wine. And women with what is fit for them, with nice clothes." And the Torah also warned us to include the poor and the strangers (converts) and the weak in the joy, as it is stated (Deuteronomy 16:14), "you, the Levite, the stranger, the orphan and the widow."
(2) It is from the roots of the commandment [that it is] because man is designed in [such] a way that his nature requires rejoicing occasionally, [just] like it requires nourishment regardless, and rest and sleep. And God wanted to give us - 'His people and the flock of His grazing' - merit and [so] commanded us to make the rejoicing for His sake, so that we could merit in all of our deeds in front of Him. And behold, He fixed for us times during the year for holidays, to remember upon them the miracles and the goodnesses that He granted us. And He commanded us then at those times to support the physical with something of joy that it needs. And it comes out as a big remedy for us that the satiation of joyous occasions be for His sake and to remember Him; as this thought will be a fence, that we do not go further out than is enough from the straight path. And the one who has reflection without a desire to argue will find reason in my words.
(3) And I have written a few of the laws of the commandment above. And the rest of its details are in Tractate Chagigah and in [various] places scattered in the Gemara.
(4) And this commandment is practiced regarding the joy - but not regarding the sacrifice - in every place and at all times by males and females. And one who transgresses it and does not rejoice himself, the members of his household and the poor according to his ability, for the sake of the commandment of the festival, has nullified this positive commandment. And in the way that we mentioned did they, may their memory be blessed, say (Avot 2:17), "All of your actions should be for the sake of Heaven."
Concurrently, to those who feel entitled (kumtzach mir), the Torah, in the terrifying tochacha, resoundingly reminds us the root of all sin, not a particular act begins with an emptiness, an unhappiness. It is as if the Torah warns:
If you can not be happy with what you have already, then who says when you get more, you will yet reach the promised land of contentment. Do you want to know why you have veered away – why you were looking for love and joy in all the wrong places? – it is because you were not able to find it at home.
In short, to gain happiness one must choose it. Like all important things in life, it is an avodah, a midah to be acquired – not a particular amount of money.
Orthodox Union- Rabbi Asher Brander
https://www.ou.org/life/torah/brander_ki_tavo_5768_be_happy/
The Arizal explains the pasuk according to the Kabbalah in a slightly different way. He says that the Torah is saying that we may have performed mitzvos with a certain degree of happiness, however our ikar joy did not derive from shemiras hamitzvos, rather from the simcha of ‘rov kol’ which refers to all other sources of happiness[3]. Thus, Hashem is telling the Jewish people that the simcha of Avodas Hashem must be far greater than the pleasure derived from other endeavors, and that this is an essential part of one’s Avoda. This is a lesson that is of great relevance to Rosh Hashanah: The main avoda of Rosh Hashanah is to make Hashem King. A significant aspect of this is to recognize that Hashem is the only source of meaning, all other ‘sources’ of pleasure are meaningless. This is also a prerequisite to the teshuva process leading up to Yom Kippur. because if a person’s sheifut (desires) are not purely towards Avodas Hashem, then he will find it almost impossible to avoid sin. There will be times when his desires clash with Ratson Hashem and his shemiras hamitzvos will inevitably suffer. Thus, any teshuva he does on Yom Kippur will be tainted by his outlook on life - that Hashem is not the only source of meaning and joy.
Rabbi Yehonasan GEFEN - © Torah-Box
[3] This Arizal was quoted by Rav Yissochor Frand Shlita
https://www.torah-box.net/parsha/deuteronomy/ki-tavo/ki-tavo-the-true-source-of-simcha_608.html

